Conventionally, various flame retardants are used in various fields to provide materials with flame retardancy. For example, a flame retardant is included in a covering material of an insulated wire for an automobile and an electric appliance.
From the view point of reducing loads on the global environment, a covering material of an insulated wire has recently been used which is prepared by adding magnesium hydroxide as a flame retardant to an olefin resin which does not emit harmful halogenous gas into the atmosphere when burned.
To such a flame-retardant composition, a large amount of magnesium hydroxide is added in order to provide sufficient flame retardancy. Because synthesized magnesium hydroxide which is synthesized using seawater for example is relatively expensive, reasonable natural magnesium hydroxide has recently been used in order to reduce the manufacturing cost.
For example, Japanese Patent No. 3339154 discloses a flame retardant prepared by pulverizing a natural mineral which is mainly composed of magnesium hydroxide and by providing surface treatment using fatty acid, fatty-acid metallic salt, a silane coupling agent, or a titanate coupling agent, a flame-retardant composition including this flame retardant, and an insulated wire coated with this flame-retardant composition.